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Chapter 5: The Biomechanics of Human Skeletal Articulations. Basic Biomechanics, 4 th edition Susan J. Hall Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University. Objectives. Categorize joints based on structure and movement capabilities.

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Chapter 5: The Biomechanics of Human Skeletal Articulations

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chapter 5 the biomechanics of human skeletal articulations

Chapter 5:The Biomechanics of Human Skeletal Articulations

Basic Biomechanics, 4th edition

Susan J. Hall

Presentation Created by

TK Koesterer, Ph.D., ATC

Humboldt State University

  • Categorize joints based on structure and movement capabilities.
  • Explain the functions of articular cartilage and fibrocartilage.
  • Describe the material properties of articular connective tissues.
  • Identify factors contributing to joint stability and flexibility.
  • Explain advantages and disadvantages of different approaches to increasing or maintaining joint flexibility.
joint architecture
Joint Architecture
  • Terms:
    • Articular Cartilage
    • Articular Capsule
    • Synovial Fluid
    • Articular Fibrocartilage
joint architecture4












Ball and socket

Joint Architecture
synovial joints
Synovial Joints
  • Categorized by number of axes of rotation
  • Capabilities of joint motion also described in terms of degree of freedom (df):
    • Uniaxial: one axis, one df
    • Biaxial: two axis, two df
    • Triaxial: three axis, three df
  • Bursae
  • Tendon Sheaths
articular cartilage
Articular Cartilage
  • Dense, white connective tissue that provides a protective lubrication.
    • 1-5 mm thick
    • Coats ends of articulating bones in diarthrodial joints
  • Purpose
    • 1) reduces amount of stress between joints
    • 2) allows movement with minimal friction and wear
articular fibrocartilage
Articular Fibrocartilage
  • In form of menisci
  • Possible purposes:
    • Distribution of loads over joint surface
    • Improvement of fit of articulating surfaces
    • Limitation of bone slip within joint
    • Protection of periphery of articulation
    • Lubrication
    • Shock Absorption
articular connective tissue
Articular Connective Tissue
  • Tendons & Ligaments
    • Composed of collagen and elastic fibers
    • Cannot contract (like muscle), are passive
    • Slightly extensible, and will return to original length after being stretched
      • Unless stretched beyond elastic limits
    • Respond to altered habitual mechanical stress by hypertrophying and atrophying
  • Ligament size proportional to is antagonists.
joint stability
Joint Stability
  • Ability of a joint to resist abnormal displacement of the articulating bones
    • To resist dislocation
    • To prevent injury to ligaments, muscles, and tendons
  • Includes:
    • Shape of articulating bone surfaces
    • Arrangement of Ligaments and Muscles
    • Other connective tissues
shape of articulating bone surfaces
Shape of Articulating Bone Surfaces
  • Articulating bone surfaces in joints of human body are all approximately reciprocal shapes.
  • Close-packed position
    • Great joint stability
    • Occurs at knee, wrist and interphalangeal joints at full extension and for the ankle at full dorsiflexion
  • Loose-packed position
    • Reduced joint stability
arrangement of ligaments and muscles
Arrangement of Ligaments and Muscles
  • Tension in ligaments and muscles contributes significantly to joint stability
    • Especially in the knee and shoulder
  • Ligament rupture or stretching can result in abnormal motion of articulating bone ends
    • Results in articular cartilage damage
  • Strong ligaments and muscles contribute to joint stability
  • Angle of Attachment
other connective tissues
Other Connective Tissues
  • Fascia
    • White fibrous connective tissue
    • Surrounds muscles and bundles of muscle fibers within muscles
    • Provides protection and support
    • Example: iliotibial band
      • Crosses lateral aspect of knee
joint flexibility
Joint Flexibility
  • Joint Flexibility
  • Range of motion (ROM)
  • Static flexibility
  • Dynamic flexibility
  • Research indicates that the two flexibility components (static and dynamic) are independent of one another
  • Flexibility is joint-specific
measuring joint range of motion
Measuring Joint Range of Motion
  • Measured directionally in units of degrees
  • In anatomical position, all joints are considered to be at zero degrees
    • Past this = hyperextension
  • ROM for extension = ROM for flexion
factors influencing joint flexibility
Factors Influencing Joint Flexibility
  • Shapes of articulating bone surfaces
  • Intervening muscle
  • Fatty tissue
  • A function of:
    • Relative laxity or extensibility of collagenous tissues and muscles crossing joint.
  • ROM inhibited by tight ligaments and muscles
flexibility injury
Flexibility & Injury
  • Hypermobile Joint
  • Limited (tight) joint flexibility can increase tearing or rupturing of collagenous tissues at joint.
  • Lax joint flexibility (low stability) leads to displacement-related injuries.
  • Flexibility decreases with aging
    • Due to decreased levels of physical activity
  • No changes in flexibility during growth in adolescence.
techniques for increasing joint flexibility
Techniques for Increasing Joint Flexibility
  • Important for therapeutic and rehabilitative programs
    • To improve/maintain joint flexibility
  • Techniques:
    • Neuromuscular Response to Stretch
    • Active and Passive Stretching
    • Ballistic and Static Stretching
    • Proprioceptive Neuromuscular Facilitation
neuromuscular response to stretch
Neuromuscular Response to Stretch
  • Golgi tendon organs (GTOs)
  • Muscle Spindle
    • Primary muscle spindle
    • Secondary muscle spindle
  • Stretch Reflex
  • Reciprocal Inhibition
  • Goal of stretching is to minimize spindle effect and maximize GTO effect.
active and passive stretching
Active and Passive Stretching
  • Active Stretching
    • Ex: to stretch hamstrings, contract quadriceps
  • Passive Stretching
    • Ex: to stretch with the force applied from another person
ballistic and static stretching
Ballistic and Static Stretching
  • Ballistic Stretching
  • Static Stretching
  • Static preferred over ballistic because ballistic activates muscle spindle response, which inhibits stretching.
  • Both forms can induce soreness in muscles not typically or habitually used.
proprioceptive neuromuscular facilitation pnf
Proprioceptive Neuromuscular Facilitation (PNF)
  • A group of stretching procedures involving alternating contraction and relaxation of the muscles being stretched.
  • Done to take advantage of GTO response.
  • Requires partner or clinician
  • Contract-relax-antagonist-contract technique
  • Agonist-contract-relax method
  • Can significantly increase joint ROM over single stretching session.
common joint injuries and pathologies
Common Joint Injuries and Pathologies
  • Due to: acute and overuse injuries, infection, degenerative conditions.
  • Sprains
  • Dislocations
  • Bursitis
  • Arthritis
  • Rheumatoid Arthritis
  • Osteoarthritis
  • Three categories of joints; synarthroses, amphiarthroses, and diarthroses
  • The ends of bones articulating at diarthrodial joints are covered with articular cartilage, which reduces contact stress and regulates lubrication
  • Fibrocartilaginous discs or menisci present at some joints also may contribute to these functions
  • Tendons and ligaments are strong collagenous tissues that are slightly extensible and elastic.
  • Tendons and ligaments are strong collagenous tissues that are slightly extensible and elastic.
  • The major factors influencing joint stability are the size and shape of the articulating bone surfaces, and the arrangement and strength of the surrounding muscles, tendons, and ligaments.
  • Joint flexibility is a function of relative tightness of the muscles and ligaments that span the joint.